Distribution and characterization of functional amiloride-sensitive sodium channels in rat tongue.

Abstract

The role of amiloride-sensitive Na + channels (ASSCs) in the transduction of salty taste stimuli in rat fungiform taste buds has been well established. Evidence for the involvement of ASSCs in salt transduction in circumvallate and foliate taste buds is, at best, contradictory. In an attempt to resolve this apparent controversy, we have begun to look for functional ASSCs in taste buds isolated from fungiform, foliate, and circumvallate papillae of male Sprague-Dawley rats. By use of a combination of whole-cell and nystatin-perforated patchclamp recording, cells within the taste bud that exhibited voltage-dependent currents, reflective of taste receptor cells (TRCs), were subsequently tested for amiloride sensitivity. TRCs were held at -70 mV, and steady-state current and input resistance were monitored during superfusion of Na+-free saline and salines containing amiloride (0.1 wM to 1 mM). Greater than 90% of all TRCs from each of the papillae responded to Na + replacement with a decrease in current and an increase in input resistance, reflective of a reduction in electrogenic Na + movement into the cell. ASSCs were found in two thirds of fungiform and in one third of foliate TRCs, whereas none of the circumvallate TRCs was amiloride sensitive. These findings indicate that the mechanism for Na + influx differs among taste bud types. All amiloride-sensitive currents had apparent inhibition constants in the submicromolar range. These results agree with afferent nerve recordings and raise the possibility that the extensive labeling of the ASSC protein and mRNA in the circumvallate papillae may reflect a pool of nonfunctional channels or a pool of channels that lacks sensitivity to amiloride.

Anion Size Does Not Compromise Sodium Recognition by Rats After Acute Sodium Depletion.

“…The sodium-selective ion channels, or epithelial sodium channels (ENaCs), expressed by these cells can be blocked with the drug amiloride (see Brand, Teeter, & Silver, 1985;DeSimone & Ferrell, 1985;Doolin & Gilbertson, 1993;Heck, Mierson, & DeSimone, 1984;Schiffman, Lockhead, & Maes, 1983). A second transduction pathway for sodium, the amiloride-insensitive (AI) pathway, is not sodium selective but instead appears to be activated by a variety of cations, including Na ϩ , K ϩ , and NH 4 ϩ (Brand et al, 1985;DeSimone & Ferrell, 1985;Kloub, Heck, & DeSimone, 1997;Ye, Heck, & DeSimone, 1994).…”

Localization of Amiloride-Sensitive Sodium Current and Voltage-Gated Calcium Currents in Rat Fungiform Taste Cells

“…Our procedure to isolate taste buds from the fungiform papillae closely followed published protocols (e.g., Doolin and Gilbertson 1996;Kossel et al 1997). Taste buds were plated on the bottom of a chamber consisting of a standard glass slide onto which a silicon ring 1-2 mm thick and 15 mm ID was pressed.…”

“…Whole cell patch-clamp recordings were made from cells in isolated taste buds as described previously (e.g., Doolin and Gilbertson 1996;Kossel et al 1997 …”

“…To this aim, we have used electrophysiological techniques (patch-clamp recording) to study the occurrence of ASSCs and voltage-gated calcium channels in taste cells and to establish whether the two classes of ion channels co-localize. Functional properties of ASSC and voltage-gated calcium currents have been studied in detail in rat fungiform papillae (Avenet and Lindemann 1991;Béhé et al 1990;Doolin and Gilbertson 1996;Furue and Yoshii 1997;Kossel et al 1997). For this reason, we analyzed the electrophysiological properties of single taste cells in taste buds isolated from rat fungiform papillae.…”

S100B‐modulated Ca2+‐dependent ROS‐GC1 transduction machinery in the gustatory epithelium: a new mechanism in gustatory transduction

“…This process occurs in the apical microvilli of the taste cells, which reside in the gustatory epithelium. The taste molecule binds to its specific receptor and initiates a cascade of molecular events, that finally result in the molecule-specific taste perception [6][7][8][9][10][11][12][13][14][15][16][17]. There are two general types of taste receptors: one, the ion channels and the other, the G-protein coupled seven-transmebrane spanning receptors.…”